We analyze PLANET collaboration data for MACHO 97-BLG-41 , the only microlensing event observed to date in which the source transits two disjoint caustics .
The PLANET data , consisting of 46 V-band and 325 I-band observations from five southern observatories , span a period from the initial alert until the end of the event .
Our data are incompatible with a static binary lens , but are well fit by a rotating binary lens of mass ratio q = 0.34 and angular separation d \approx 0.5 ( in units of the Einstein ring radius ) in which the binary separation changes in size by \delta d = -0.070 \pm 0.009 and in orientation by \delta \theta = 5 ^ { \circ } \hskip { -2.0 pt } .61 \pm 0 ^ { \circ } \hskip { -2.0 pt } .36 during the 35.17 days between the separate caustic transits .
We use this measurement combined with other observational constraints to derive the first kinematic estimate of the mass , distance , and period of a binary microlens .
The relative probability distributions for these parameters peak at a total lens mass M \sim 0.3 M _ { \odot } ( M-dwarf binary system ) , lens distance D _ { L } \sim 5.5 kpc , and binary period P \sim 1.5 yr .
The robustness of our model is demonstrated by its striking agreement with MACHO/GMAN data that cover several sharp features in the light curve not probed by the PLANET observations , and which did not enter our modeling procedure in any way .
Available data sets thus indicate that the light curve of MACHO 97-BLG-41 can be modeled as a source crossing two caustics of a physically-realistic rotating binary so that , contrary to a recent suggestion , the additional effects of a postulated planetary companion to the binary lens are not required .